ACCELERATION OF STRENGTH GAIN OF LIME-POZZOLAN CEMENTS BY THERMAL-ACTIVATION

This paper deals with the effect of curing temperature on: (a) the tim e for development of appreciable strength, (b) ultimate strength and ( c) strength development rate of lime-natural pozzolan cement pastes wi th and without chemical activator (4% Na2SO4 and 4% CaCl2.2H2O). The r esults indicate that the initial hardening time (time for pastes to ac hieve significant strength) decreases noticeably as the curing tempera ture rises. The ultimate strength of these cement pastes indirectly sh ows good linear correlation with the curing temperature; the rate of s trength development fits the Arrhenius equation well. The addition of 4% Na2SO4 does not change the initial hardening time, but can increase both the strength gain rate and ultimate strength by 50 to 90%. The p resence of 4% CaCl2.2H2O greatly improves the ultimate strength - by 2 or more times compared to the control pastes; initial hardening time, however, increases. Based on the strength development rate constants and the Arrhenius equation, the apparent activation energies of the co ntrol pastes, pastes with 4% Na2SO4 and the pastes with 4% CaCl2.2H2O are 66, 75 and 99 KJ/mol respectively.